A large number of very valuable analgesic antipyretics have found a definite place in practical medicine. Their number is liable to increase very materially. In general the pharmacodynamic action of all of the aniline derivatives is similar. They are all poisonous, but their toxic actions will vary, largely, depending on dosage, on the nature of the substituted radicle, on the position in the molecule of the substituted radicle. In all of the anilines the skin, the digestive tract, the nervous system, and the blood are affected. Skin eruptions are various, herpes, urticaria, prurigo, pemphigus, ecthyma, or eczema may be encountered.

The digestive symptoms are numerous and variable. Anorexia is common, constipation is also characteristic; nausea and vomiting not infrequent.

The nervous system may present symptoms of paresis or paralysis of the voluntary muscles particularly, and analgesic action is constant for all of the anilines.

The blood-changes induced by this group are of extreme importance. They may consist of oxygen fixation with the formation of methemoglobin or even of hemolysis, with methemoglobin production. These blood-changes are largely due to the action of para-amido-phenol, into which, or compounds of which, practically all of the derivatives of this series are broken down.

The number of these compounds is so numerous that only those that have been clinically valuable can be mentioned. The chief of the earlier members of this group is acetanilid.